A cross-point memory device which includes a variable resistive element has potential for realizing a nonvolatile memory device with a high storage density. These memory devices store information by setting the data to correspond with the resistance value of a variable resistive element. For example, Phase Change Random Access Memory (PCRAM) stores data by causing a phase change material in a storage medium from a crystalline condition (Conductor) to an amorphous state (Insulator), thus, altering a resistance value of the material. A Resistive RAM Memory (ReRAM) writes data by altering the resistance value of a transition metal oxide whose resistance changes when a voltage is applied. A Conductive Bridging RAM (CBRAM) operates by changing a resistance value in a storage medium by bridging an insulating layer between electrodes by the reduction of metal ions. Other memory types are also known.
Among its advantages, a CBRAM is generally composed of the same materials as a standard semiconductor memory device (e.g., NAND Flash) and also shares a common manufacturing process with standard semiconductor devices. Furthermore, the CBRAM requires very little writing current and deleting current in operation, and has good data retention properties. For these reasons, it is expected to be appropriate as a memory cell for a cross-point memory device having a high storage capacity. However, the CBRAM suffers the disadvantage of an increasing leakage current when the reduction of metal ions becomes excessive in the resistance switching (change) layer. Also, if the resistance switching layer is made thicker to reduce the leakage current, the writing (set) voltage will increase.